Characterization of microRNAs expressed in the developing songbird brain Project Summary Many parallels are shared between language development in human children and song learning in songbirds. Thus songbirds provide a unique model system to study the molecular and cellular mechanisms controlling neural circuit development and vocal learning. MicroRNAs are a class of non-protein coding RNA molecules that regulate gene expression post transcriptionally in a wide array of biological events, especially during development. We plan to study the regulatory functions of miRNAs in neural development and plasticity in zebra finches, where both the song behavior and the underlying neural circuits have been extensively established. In this two-year exploratory project, we will focus on a systematic genome-wide characterization of miRNA expression in the zebra finch brain across a bird's entire life span. This project has two specific aims. In Specific Aim I, small RNA libraries from zebra finch brains at different developmental stages ranging from the early embryonic stage to old age will be made;the libraries will be sequenced using the ultra-high-throughput Solexa sequencing technology;miRNA candidate sequences will be annotated with Bioinformatic analysis. In Specific Aim II, Northern blot hybridization and in situ hybridization will be performed for a selected group of miRNA candidates to validate their expression and to map their expression to the song control nuclei during circuit development. Priorities will be given to miRNAs that have been implicated in neural development, plasticity, and developmental disorders, as well as miRNAs whose predicted target genes have been implicated in these processes. This initial experiment will generate necessary information (e.g., the temporal and spatial miRNA expression in the developing song system), thus setting up the stage for our longer-range research on the roles of miRNAs in neural development/plasticity and in developmental disorders. A systematic genome-wide miRNA profiling in the songbird brain may extend the miRNA repertoire and their expression patterns during development may provide insights to their functions. In addition to our own work, the experimentally identified miRNA sequences may be used in the annotation of the zebra finch genome sequence. Also, comparative analysis of miRNAs in songbirds and other species may add to our understanding of the evolution of miRNA gene family in general. PUBLIC HEALTH RELEVANCE: MicroRNAs regulate gene expression and play important roles in brain development;therefore, understanding the molecular mechanisms of miRNA function is essential for understanding normal brain developmental processes and developmental disorders. The importance of miRNA research has been exemplified by the fact that currently there are already several RNAi-based drugs being tested in clinical trials for illnesses ranging from cancer to eye disease. Results from our experiment, where miRNAs are studied in the context of neural circuit development and vocal learning, may contribute to understanding and eventually curing developmental disorders in human children (e.g., autism, dyslexia, etc).